Theoretical and Experimental Investigations on the Frequency-Tunable Terahertz Gyrotron

Theoretical and experimental investigations on a frequency-tunable terahertz gyrotron have been presented in this paper. The effects of the slightly up-tapered sections in an improved multi-section gyrotron cavity on the resonant frequency and the quality factor are investigated in detail. In an optimized multi-section gyrotron cavity, the quality factor for all axial modes can maintain an order of magnitude in the cold cavity approximation, it means that the operating current for all axial modes can keep an order of magnitude. A resonator-based gyrotron oscillator can play dual functions: gyromonotron and reflected-type gyro-BWO corresponding to forward-wave and backward-wave operation. the field profile of the axial mode and beam-wave interaction efficiency of the gyromonotron and the reflected-type gyro-BWO are dramatically different from each other. And the gyromonotron state can switch to the reflected-type gyro-BWO state by means of increasing the operating magnetic field. A 263GHz frequency-tunable gyrotron at the fundamental cyclotron harmonic for the 400MHz DNP/NMR spectroscopy and a 527GHz frequency-tunable gyrotron at the second cyclotron harmonic for the 800MHz DNP/NMR spectroscopy are experimentally investigated.